# Chapter 2 - PowerPoint PPT Presentation

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Chapter 2. Scientific Method. Scientific Method. Scientific method- logical approach to solving problems by observing & collecting data, formulating hypotheses, testing hypotheses, formulating theories supported by data Examples of problems… Observable data

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Chapter 2

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## Chapter 2

Scientific Method

### Scientific Method

• Scientific method- logical approach to solving problems by observing & collecting data, formulating hypotheses, testing hypotheses, formulating theories supported by data

• Examples of problems…

• Observable data

• Qualitative = descriptive (turn pink)

• Quantitative = numerical (1 gram)

### Data

• We cannot observe everything all at once, so we focus on a system

• System- specific portion of matter chosen for study (ex. Reaction in a test tube)

• Once we obtain data, we can establish patterns

• Patterns can be made into scatter plots, bar graphs, pie charts, etc.

### Hypothesis

• Once we have looked for patterns, we form a hypothesis

• Hypothesis- testable statement in the form of “if…then…”

• Then we have to test the hypothesis

• Control(s)- stay constant (placebo)

• Variable(s)- change, only changed one at a time

• If wrong, change or drop hypothesis (might start over)

### Hypothesis (con.)

• If correct, explain through models

• Model- explains how events occur or are related in a visual, verbal, or mathematical way

• Theory- broad generalization that explains group of facts or events

• Publish results (letters, scholarly journals, blog, word of mouth)

### Metric System

• SI, or SystèmeInternationaled’Unités (French)

• Base units

• Length (lowercase L) = meter (m)

• Mass (m) = kg (kilogram)

• Time (t) = second (s)

• Temperature (T) = Kelvin (K)

• Amount of substance (n) = mole (mol)

• Electric current (I) = ampere (A)

• Luminous intensity (Iv) = candela (cd)

### Metric prefixes

• Mega (M) = 10 6

• Kilo (k) = 10 3

• Hecto (h) = 10 2

• Deka (da) = 10 1

• Deci (d) = 10 -1

• Centi (c) = 10 -2

• Milli (m) = 10 -3

• Micro (µ) = 10 -6

• Practice problems on board

### Mass vs. Weight

• Mass = amount of matter

• Weight = amount of gravity pull

• On moon, gravity 1/6 that of Earth

• Didn’t lose mass, lost weight

### Derived SI units

• Combinations of base units

• Area (A) = lxw = m2 or cm2

• Volume (V) = lxwxh = m3 or cm3

• Density (D) = kg/m3 or g/cm3 or g/mL

• Molar Mass (MM) = kg/mol

• Energy (E) = Joule (J)

### Accuracy vs. Precision

• Accuracy- close to accepted value

• Precision- close to measurements made in same way

• Drawings on board

### Percent Error

• Goal = 0

• (Experimental – Accepted)/(Accepted) x 100

• Problems on board

### Significant figures

• All digits but last one certain

• Rules

• Nonzero = significant

• Zero in between nonzero (2002) = significant

• Zero in front of nonzero = not significant

• Zero at end of number and to right of decimal = significant

• Ex. 2000 = 1 sig, 25.00 = 4 sig, .0001 = 1 sig

• Examples on board

### Rounding

• 1->4, round down

• 6->9, round up

• 3.5->4

• 4.5->4

• Sig + or – Sig= same # of decimals

• Sig x or / Sig = same # of sig digits

• Examples on board